A known image forming apparatus includes an image carrier and a transfer member. The image forming apparatus is configured to transfer a toner image on the image carrier onto a sheet that passes between the image carrier and the transfer member, by controlling power supply to the transfer member. To prevent or reduce poor transfer, the image forming apparatus is configured to switch a power supply control to the transfer member from a constant current control to a constant voltage control, and vice versa, when a resistance value of the transfer member exceeds a reference limiting value.